Vinylidene chloride polymers have excellent barrier properties to a wide variety of gases and liquids due to the combination of high density and high crystallinity of the polymers. Extruded or coated PVdC products with superior resistance to most gases like oxygen are used in packaging. However, PVdC materials are subject to thermal instability. Thermal degradation by dehydrochlorination can be promoted by metals, such as zinc, copper and iron (steel).
During extrusion of polyolefins containing PVdC on conventional equipment, thermal degradation is a problem. For example, blends of polypropylene and PVdC are processed at temperatures of about 160.degree.-165.degree. C. and up to 220.degree. C. Thermal degradation by dehydrochlorination of PVdC occurs at temperatures above 120.degree. C. on conventional equipment; at temperatures about 170.degree. C. carbon black builds up; build up of the carbon black can also result in break off of carbon which contaminates the extrudate with black specks; at 165.degree. C. this carbon build up may result in a black extrudate. The dehydrochlorination of the PVdC is, by definition, accompanied by the evolution of hydrochloric acid. This elimination of HCl, molecular components of atoms of the PVdC, also results in holes in the extrudate.
One of the recommended ways of eliminating the problems of thermal degradation of the PVdC on extrusion is to use metals and/or alloys of other than steel or iron containing extrusion equipment, dies, screw and barrel. Dies, screw(s) and barrels made out of materials other than steel and iron eliminate the aspect of the iron (steel and/or zinc and/or copper) promoted dehydrochlorination of PVdC. However, this is a costly alternative for eliminating decomposition of the PVdC contained on the polypropylene extrudate or blended therein.